A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the determination of 56 residual pesticides from commercial crops. For a validation of the method, the recoveries, linearities, limits of detection (LOD), and limits of quantitation (LOQ) of the 56 pesticides were investigated. The linearities, LOD, and mean recoveries of the pesticides ranged 0.9686-0.9999, $0.00-11.54{mu}g/kg$, and 65-82%, respectively. This method was evaluated by its application to monitor 345 agricultural products collected from 9 provinces in Korea 2011. Fifteen pesticides were detected from 39 samples and 2 or more residual pesticides were found in 7 samples. However, none of the compounds were observed above the corresponding maximum residue level. The results reflect that the detected pesticide residues were in a safe range and that residual pesticides in the agricultural products in Korea were properly controlled.